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Performance Capabilities for Internal Exposure Monitoring cont'd - doe-std-1128-98_ch10117
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DOE Standard Guide of Good Practices for Occupational Radiological Protection In Plutonium Facilities
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Scope of Bioassay Program - doe-std-1128-98_ch10119


DOE-STD-1128-98
Doses should be calculated and recorded for any confirmed plutonium intake. What
constitutes a confirmed intake is discussed in Section 5.7. Along with the doses,
supporting records must be maintained, including the bioassay data, assumptions,
biokinetic models, and calculational methods used to estimate the doses. These may
be included in letter-report dose assessments, databases, technical basis documents,
and similar records, either singly or in combination.
5.1.2
Protection of the Embryo/Fetus, Minors, and Members of the Public
The dose equivalent limit for the embryo/fetus of a declared pregnant worker is 0.5
rem for the entire gestation period, defined as the summation of external dose
received and internal dose received during the gestation period (not the 50-year
committed internal dose). Internal exposure monitoring is required if an intake is
likely to result in more than 10% of that limit (i.e., 50 mrem for the gestation period).
As discussed in more detail in Section 5.6., providing adequate protection to keep the
mother's intakes below the occupational limits will also provide adequate protection
for the embryo/fetus. Thus, special bioassay for plutonium or americium related to
pregnancy is not required. As a matter of caution, some sites try to obtain baseline
bioassays as soon as a pregnancy is declared, with another baseline bioassay
following the end of pregnancy. Some sites also offer to restrict pregnant workers
from jobs with relatively high potential for occupational intakes.
Minors and members of the public are limited, in part, by 10 CFR 835.207 and 10
CFR 835.208 (DOE, 1998a) to a TEDE of 0.1 rem/year. Internal exposure
monitoring is required if an intake is likely to result in 50% of that limit (0.05 rem).
As noted in Section 5.1.1, because bioassay monitoring is not likely to be sufficiently
sensitive to identify such intakes on a routine basis, enhanced workplace surveillance
or restriction of access may be required.
5.2
CHARACTERIZATION OF INTERNAL HAZARDS
Plutonium can be encountered in a wide range of mixtures, e.g., a pure isotope in a standard
solution, a highly variable combination of isotopes in so-called "weapons grade" or "fuels
grade" Pu, or commercial spent fuel. In addition, the age of a mixture significantly affects
its isotopic composition. As a typical weapons or fuels grade mixture ages, the 241Pu decays
to 241Am. Although the mass changes may be quite small, the overall result can be a
significant build-up of 241Am radioactivity with time. This buildup can make the mixture
somewhat easier to detect by in vivo methods. Table 5.4 shows some example plutonium
mixtures which might be encountered in DOE facilities. Isotopically pure forms of
radionuclides can also be encountered. Table 5.5 demonstrates the impact of aging on the
activity composition of two mixtures. The composition of plutonium in the facility can
significantly affect the design and capabilities of an internal dosimetry program. As part of
the program technical basis, the plutonium mixtures need to be determined. In addition,
determinations should be made at the time of identified incidents of potential intake.
Methods for such determination may include radiochemical analysis or chemistry followed
by mass spectrometry.
The physical-chemical form of plutonium also affects the internal hazard posed. Oxides of
plutonium tend to exhibit inhalation class Y behavior, whereas other compounds such as
nitrates are assigned class W by the ICRP. However, as noted in Section 2.4.1, extremes
5-8


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